The present invention relates to agricultural machinery; and more particularly, it relates to a spring reset mechanism for enabling a ground-engaging tool to raise upon striking an obstacle, elevate above the obstacle to clear it, and then reset to its original working depth automatically and under predetermined force provided by a spring mechanism.
The spring mechanism of the present invention may be adapted to a wide range of agricultural tools, including tillage tools such as moldboard plows, chisel plows and field cultivator shanks; but it is also adaptable for other ground-engaging tools such as fertilizer knives, ridging devices, furrow-openers or the like.
With the greater power and higher operating speeds of modern agricultural tractors, some prior mechanisms for permitting ground-engaging tools to clear obstacles such as rocks, have become unsuitable for field use. Such mechanisms, which are broadly referred to as reset mechanisms, may be classified into three general types. One type, called a trip mechanism, has a threshold force which is determined by a mechanical device or arrangement, perhaps including a detent, which requires that the threshold force be exceeded even before the mechanism will allow the tool to elevate. Obviously, when the tool first encounters increased resistance, the resistance could be caused either by a change in soil conditions or engagement with a rock. Mechanisms which employ a mechanical threshold which must be overcome before the tool can be elevated may result in breakage because of the extremely quick reaction time that must be provided and the fact that the mechanical mechanism must release after the tripping force is encountered before the tool can clear the obstruction. Once the trip force is exceeded, obviously, it is desirable to have the mechanism react very quickly and without a substantial increase in resistance force. A further disadvantage of mechanical trip mechanisms is that the farmer must stop the tractor and reset the mechanism manually after it has tripped.
A second type of reset mechanism is called an automatic reset mechanism. In this type of protective mechanism, a mechanical device may define the trip threshold as with the first type described above, but a spring is used to reset the mechanism so the farmer does not have to do it individually.
A third type of protective reset mechanisms includes spring cushion devices. These safety mechanisms generally include a threshold force that is determined by the preload on one or more springs, and once it is overcome, the springs compress. These devices enable a quick reaction time for the mechanism to clear obstructions, but designs of this type can suffer from one or more disadvantages. One disadvantage might be that the reset force continues to increase at the same rate as the tool is elevated. This is caused primarily by the fact that the mechanism continues to compress the spring at the same rate for the entire vertical displacement of the tool. Another problem in spring cushion mechanisms is that if the preload is not properly adjusted, the entire machine may not function properly. If the preload, for example, is too low for soil conditions, then the mechanism will float--that is, during operation, individual devices will compress even though an obstruction has not been encountered. When this happens, the entire frame of the implement can vibrate, resulting in a staggered motion or "duck walking" of the implement and improper operation.